If you've decided that the risk of head injury when you walk somewhere is so little that you'll take the risk and not wear the helmet, you've made the exact same decision as the cyclists. In the Netherlands, because they have a sensible traffic system, the risk has been reduced so far that many, many people make that same decision that you do when you walk without wearing a helmet.
And I've experienced that a cycling helmet is good to wear. There was this child that appeared from a bush to the bike path. I hit the brakes and went over the bar. A slight bumb in the head but no injury there; broke a radix bone though.
Please do not be offended, and by all means keep on wearing a helmet if you want (after all it is safer, no denying that) but maybe there is room for improvement in your cycling? Those two things I quoted seem to indicate you haven't completely mastered cycling, or your bike isn't properly setup, or a combination of both. I see them for instance as well with foreigners who never owned a bycicle and then come to a country and are given one. For an experienced byciclist riding is usually a second nature, like walking, and falls don't happen more often then they do with walking. Note I'm talking 'normal' cycling here, not for instance downhill or bmx where not ever falling sometimes means you're not pushing yourself hard enough :]
And since bikes don't have ABS, I either have brakes that are not powerful enough, or I have brakes that throw me over the bar if I a mistake in a surprising situation (such as in the case I mentioned). Most falls I have are due to ice. Every winter morning is a decision: do I take the bike with studded tyres, or the one that is much lighter to ride? Sometimes I make the wrong assessment.
Other people made the decision that they're happy with the risk of not wearing a helmet when cycling.
What is so special about you? Are you some kind of super-powered genius, and your assessment of personal risk is some kind of magically "absolutely correct" answer? Why should your personal choice about acceptable risk be made law? (Trick question; it shouldn't)